Elevated tumor necrosis factor-alpha in skeletal muscle after stroke

Tumor necrosis factor-alpha (TNF-alpha), an inflammatory cytokine negligibly expressed in normal muscle, is elevated in selected metabolic conditions characterized by muscle wasting and insulin resistance. Inflammation is fundamental to stroke pathogenesis. Stroke patients have gross muscular atrophy and high prevalence of diabetes and insulin resistance. Yet, no previous studies examined TNF-alpha expression in hemiparetic skeletal muscle. This study investigates whether TNF-alpha mRNA levels are elevated in paretic compared with nonparetic leg muscles of chronic ischemic stroke patients and age-matched controls.

Total RNA extracted from bilateral vastus lateralis muscle biopsies from n=20 hemiparetic stroke patients and n=9 healthy controls was reverse transcribed to cDNA, then TNF-alpha transcripts were amplified by real-time quantitative polymerase chain reaction. TNF-alpha mRNA concentrations were normalized against acidic ribosomal phosphoprotein, housekeeping gene.

TNF-alpha mRNA levels were 2.8-fold higher in paretic compared with control leg muscle (6.28+/-1.86 versus 2.28+/-0.67; P<0.03) and 1.6-fold higher in nonparetic leg (3.71+/-1.02; P<0.11) compared with controls. There was a trend for higher TNF-alpha mRNA in paretic compared with nonparetic leg.

Findings demonstrate increased TNF-alpha expression in paretic leg muscle, suggesting inflammatory pathways are accelerated in stroke muscle. Further studies are under way to determine whether intramuscular TNF-alpha contributes to atrophy and metabolic abnormalities after stroke.